Functional fluids



United States Patent n FUNCTIONAL FLUIDS Harry R. Gamrath and Roger E. Hatton, St. Louis, Mo., assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application November 15, 1950, Serial No. 195,913

8 Claims. (Cl. 252-78) This invention relates to functional fluids; more specifically, this invention relates to improved functional fluid compositions comprising a mixture of dialkyl monoaryl phosphate esters having the formula II m-o-r-o-m R4OOC (CH2) nCOOR wherein R4 and R5 represent alkyl radicals containing from 4 to carbon atoms and n is an integer from 2 to 8 inclusive.

Many different types of materials are utilized as, functional fluids and functional fluids are used in many different types of applications. Such fluids have been used as synthetic lubricants, damping fluids, bases for greases, force transmission fluids (hydraulic fluids) and as filter mediums for air conditioning systems. Because of the wide variety of application and the varied conditions under which functional fluids are utilized, the properties desired in a good functional fluid necessarily vary with the particular application in which it is to be utilized with each individual application calling for a functional fluid having a specific class of properties. Of primary importance in a functional fluid is its viscosity characteris tic over a wide temperature range and blends of different types of functional fluids are often resorted to in order to obtain a particular functional fluid having a particular viscosity characteristic. Knowing the viscosity characteristics of two separate functional fluids, it has heretofore been possible in the case of certain materials to determine the ratio in which these two fluids must be combined in order to obtain a new fluid having viscosity characteristics intermediate or resulting from the two individual functional fluids. ASTM Method D34l-43, Appendix, has afforded a convenient method in certain instances of determining or predicting the viscosity characteristics of a mixture composed of two functional fluids whose viscosity characteristics individually are known.

Various esters of ortho-phosphoric acid and of alipredicted viscosity of the mixture when determined in phatic dicarboxylic acids have been found to have utility as functional fluids. Among the ortho-phosphate esters, we have found that the dialkyl monoaryl phosphates as a class possess exceptional properties in functional fluids. Such dialkyl monoaryl phosphates are superior to the trialkyl phosphates because they are generally less volatile. The dialkyl monoaryl phosphate esters are superior to the triaryl phosphates and the monoalkyl diaryl phosphates because they possess improved viscosity characteristics at low temperatures. It has been found that the dialkyl monoaryl phosphate esters may be utilized individually as functional fluids or mixtures of the dialkyl monoaryl phosphate esters may be utilized to obtain functional fluids having particular viscosity characteristics unattainable by the phosphate esters individually, but obtainable through mixtures of the phosphate esters. When utilized as mixtures, the mixtures have been found to behave as would be expected or predicted. In other words, the actual viscosity of monoaryl phosphate esters is essentially the same as the --of transmitting power accordance with ASTM Method D341-43. In like fashon, the alkyl esters of aliphatic dicarboxylic acids are utillzed individually in certain applications as functional flulds, while in others, mixtures of the alkyl esters of aliphat1c dicarboxylic acids are utilized in order to obtain a particular viscosity characteristic. As in the case of mixtures of the dialkyl monoaryl phosphate esters, mixtures of the esters of aliphatic dicarboxylic acids have been found to behave as would expected in that the actual viscoslty of such mixtures is essentially the same as the predlcted viscosity when determined in accordance with ASTM Method D341-43. The viscosity characteristics of such compositions are illustrated in the following Table A:

TABLE A V Viscosity in Centistokes at 40 F. Composition Observed Predicted Di-n-butyl suceinate "18. 9 Diamyl adinate 1 92 Di(6-methylheotyl) adipate. 1, 270 Di(2-ethy1hexyl) sebacate 1, 600 Z-Ethylhexyl n-butyl phenyl phospha 641 2-1Ethylhexyl eapryl phenyl phosphate- 1, 710 D1(2-ethylhexyl) phenyl phosphate 1 a 820 161 2-Ethylhexyl n-butyl eresyl phosphate l, 370 2-Ethylhexyl see-butyl cresyl phosphate 3, 500 2-Ethylhexyl Z-butyloctyl eresyl phosphate..." 6, 200 50% Diamyl adipete 503 510 50% Di(2-ethylhexyl) sebaeate 50% Diamyl adipate 512 495 50% DitG-methylheptyl) adipa 50% 2-Ethy1hexyln-butylphenyl phosphate-.- 1 090 1 50% Di(2-ethylhexyl) phenyl phosphate 50% 2-Ethylhexyl n-bntyl eresyl phosphate- 2 850 2 800 50% 2-Ethylhexy1 Z-butyloetyleresylphosphate.

* Viscosity at 0 F.

hand find much wider utility because of their excellent fire-retardency and relatively low viscosity at low temperatures. However, notwithstanding the favorable properties exhibited by the dialkyl monoaryl phosphate esters, certain functional fluid applicationsrequire a relatively non-flammable functional fluid having even a lower viscosity at monoaryl phosphate esters per se.

It is an object of this invention to provide new and improved compositions having utility as functional fluids. It is a further object of this invention to provide new and improved compositions having increased utility as functional fluids at low temperatures. A still further object of this invention is to provide an improved method in and lubricating the frictional parts of a hydraulic system having a pump therein supplying the power. Another object of this invention is to provide a hydraulic system having improved performance characteristics. Further, objects, will become apparent from a description of thisinvention.

It has now been discovered that mixtures of the dialkyl monoaryl phosphate esters hereinbefore described and 'the dialkyl esters of aliphatic dicarboxylic acids hereinbefore described behave abnormally in that the viscosity 'of such mixtures does not correspond to the predicted value, but is actually much lower, resulting in functional fluids having unexpected, unpredictable and surprisingly enhanced physical properties. ment of this invention, therefore, improved functional fluids, characterized by exceptionally low viscosity characteristics at low temperatures and excellent fire-retard: ency, comprising a mixture'of the dialkyl monoaryl phosphate esters hereinbefore described and the dialkyl esters of aliphatic dicarboxylic acids hereinbefore described are provided. The following examples are illustrative, but

Patented Jan. 4,1955.

low temperatures than do the dialkyl According to one embod1- not limitative, of the novel improved functional fluids of this invention:

Example I An improved functional: fluid. was prepared by mixing parts by weight of diamyl adipate and 90 parts by weight of di(2-ethylhexyl) phenyl phosphate. The resultant functional fluid had the following properties:

Specific gravity at /25 C 0.9875 1.4659.

Pour point Below 70 F. Viscosity, centistokes:

At 210 F 2.21.

At 100 F 8.02.

At 40 F 1340.. Predicted viscosity at 40 F 1450.

Example II An improved functional fluid was prepared by mixing 10 parts by weight of di-isoamyl adipate and 90 parts by weight of Z-ethylhexyl n-butyl phenyl phosphate. The resultant functional fluid had the following properties:

Specific gravity at25/25 C 1.0129. N 1.4663. Pour point Below -70. F. Viscosity, centistokes:

At 210 F 1.82. At 100 F 5.93.

Example III An improved functional fluid was prepared by mixing 10 parts by weight of di(6-methylheptyl) adipate and 90 parts by Weight of Z-ethylhexyl sec-butyl p-chlorophenyl phosphate. The resultant functional fluid had the following properties:

Specific gravity at 25'/25 C 1.0756. N 25 1.4800. Pour point Below -70 F. Viscosity, centistokes:

At 210 F 2.53.

At 100 F 11.07.

Example IV An improved functional fluid was prepared by mixing 25 parts by weight of diamyl adipate and 75 parts by weight of 2-cthylhexyl capryl phenyl phosphate. The resultant functional fluid had the following properties:

Specific gravity at 25 /25 C 0.9776. N 25 1.4600. Pour point Below 70 F. Viscosity, centistokes:

At 210 F 2.10. At 100 F 7.33. At -40 F 857. Predicted viscosity at -40 F 1000.

Example V An improved functional fluid was prepared by mixing 25 parts by weight of di(Z-ethylbutyl). adipate and 75 parts by weight of n-octyl n-butyl phenyl phosphate. The resultant functional fluid had the following properties:

Specific gravity at 25/25" C 0.9955. N 1.4605.

Pour point Below -70' Viscosity, centistokes:

At 210 F. 1.92.

At 100 F. 6.03.

Example VI An improved functional fluid was prepared by mixing 50 parts by weight of di-isoamyl adipate and 50 parts by weight of Z-ethylhexyl n-butyl phenyl phosphate. The resultant functional fluid had the following properties:

Specific gravity at 25/25 C 0.9809. N 25 1.4518. Pour point Below 70 F. Viscosity, centistokes: At 210 F 1.73. At 100 F 5.29. At 0 F 49.7. At 40 F 327.

Predicted viscosity at -40 F 370.

4 Example VII An improved functional fluid was prepared by mixing 50 parts by weight of diamyl adipate and 50 parts by weight of 2-ethylhexyl sec-butyl cresyl phosphate. The resultant functional fluid had the following properties:

Specific gravity at 25/25 C 0.9780. N 25 1.4541. Pour point Below 70 .F. Viscosity, centistokes:

At 210 F 2.07. At F 6.68. At.40 F 537. Predicted viscosity at 40F 750.

Example VIII An improved functional fluid was prepared by mixing 50 parts by weight of di(2-ethylbutyl) adipate and 50 parts by weight of 2-ethylhexyl isobutyl phenyl pho N hate. The resultant functionalfluid had the following properties:

Specific gravity at 25/25 C 0.9828. N 25 1.4560. Pour point Below 70 F. Viscosity, centistokes:

At 210 F 2.74.

At 100 F 6.19.

At 40 F 525. Predicted'viscosity at 40 F 640.

Example IX An improved functional fluid was prepared by mixing 50 parts by weight of di(Z-ethylbutyl) adipatc and 50 parts. by weight of n-butyl sec-tetradecyl phenyl phosphate. The resultant functional fluid had the following properties:

An improved functional fluid was prepared mixing 50 parts by weight of di(-methylheptyl) adipatc 50 parts by weight of Z-ethylhexyl capryl phenyl phosz The resultant functional fluid had the following pro Specific gravity at 25/25 C 0.9565. N 25 1.4570. Pour point Below ---70 It. Viscosity, centistokes:

At210 F 2.53. At 100 F 9.21. At --40 F 1360. Predicted viscosity at 40 F 1475.

Example XI An improved functional fluid was prepared by mixing 50 parts by weight of di-n-butyl adipate and 50 parts by weight of di(Z-ethylhexyl) phenyl phosphate. The resultant functional fluid had the following properties:

Specific gravity at 25/25 C 0.9735 N 25 1.4496 Viscosity, centistokes: t 210 F. 1.6)

At 100 F. 5.0

At 40 F. 42

At 0" F. 42.5 Predicted viscosity at 0 F. 57.0

The predicted and observed viscosities of this composition were compared at 0 F. since di-n-butyl adipate crystallizes at about 9 F.

7 Example XII An improved functional fluid was prepared by mixing 50 parts by weight of di(Z-ethylhexyl) sebacate and 50 parts by weight of Z-ethylhexyl n-butyl phenyl phosphate. The resultant functional fluid had the following properties:

Specific gravity at 25 25 C 0.9648. N 1.4587. Pour point Below -70 F. Viscosity, centistokes:

At 210 F 2.49. At 100 F 8.87.

Example XIH An improved functional fluid was prepared by mixing 50 parts by weight of di(2-ethylhexyl) sebacate and 50 pgrts by weight of 2-ethylhexyl 2-buty1octyl cresyl phosp ate.

properties:

Specific gravity at 25 /25 C 0.9362. N 1.4588. Pour point Below -70 F. Viscosity, centistokes:

At 210 F 3.57.

At 100 F 13.69.

At -40 F 2840. Predicted viscosity at 40 F 3150.

Example XIV An improved functional fluid was prepared by mixing 50 parts by weight of di-n-butyl succinate and 50 parts by weight of di(2-ethylhexyl) phenyl phosphate. The

resultant functional fluid had the following properties:

Specific gravity at 25 /25 C 0.9833 N 25 1.4481 Viscosity, centistokes:

At 210 F 1.68 At 100 F 4.98 At 40 F 284 At F 43.6 Predicted viscosity at 0 F 50.5

The predicted and observed viscosities of this composition were compared at 0 F. since di-n-butyl succinate crystallizes at about 19 F.

In addition to the dialkyl monoaryl phosphate esters utilized in the preceding examples, the following orthophosphate esters are further examples of dialkyl monoaryl phosphate esters which may be utilized to prepare improved functional fluids in accordance with this invention:

DIALKYL MONOARYL ORTHO-PHOSPHATE ESTERS While those dialkyl monoaryl phosphate esters wherein the alkyl substituents are unsubstituted constitute a preferred embodiment of this invention, the alkyl substituents may be substituted with one or more unreactive substituents. Thus, the alkyl groups of the hereinbefore described phosphate esters may be substituted with nitro groups, aryl groups such as phenyl, alkoxy groups such as ethoxy, butoxy, isopropoxy, etc. In like manner, those dialkyl monoaryl phosphate esters wherein the aryl group is a phenyl group, which may be substituted or unsubstituted, constitutes a preferred embodiment of this invention. Typical of such aryl groups are the phenyl, cresyl, higher alkyl substituted phenyl, alkoxy substituted. phenyl, halogen substituted phenyl and nitro substituted phenyl groups.

The novel functional fluids of this invention may be prepared by merely mixing the dialkyl monoaryl phosphate esters hereinbefore described and the dialkyl esters of aliphatic dicarboxylic acids in any desired proportion, dependent upon the resultant physical properties desired. A particularly preferred class of functional fluids exhibiting significantly enhanced physical properties are those containing the hereinbefore described dialkyl monoaryl The resultant functional fluid had the following phosphate esters and from about .5 to about 75% by weight of total composition of a dialkyl ester of an aliphatic dicarboxylic acid.

The novel functional fluids of this invention comprising a mixture of the hereinbefore described dialkyl mono: aryl phosphate esters and dialkyl esters of aliphatic dicarboxylic acids may be used per se as functional fluids or they may be used in combination with oxidation inhibitors, rust inhibitors, anti-foaming agents, detergents, viscosity index improvers compatible therewith, etc., whenever specific uses require such addition agents. Particularly useful functional fluids are those compositions comprising a mixture of a hereinbefore described dialkyl monoaryl phosphate ester, a dialkyl ester of an aliphatic dicarboxylic acid and a minor amount, such as from about 0.2 to about 10% by weight of total composition of a viscosity index improver, such as a poly-' merized alkyl methacrylate (preferably the poly octyl methacrylate) or an alkylated polymerized styrene, such as polymerized styrene of a molecular weight within the range of 10,000 to 150,000 which has been alkylated with olefins containing from 6 to 15 carbon atoms.

As a result of the excellent physical properties of the functional fluids particularly described in the preceding examples, improved hydraulic pressure devices can be prepared in accordance with this invention which comprise in combination a fluid chamber and an actuating fluid in said chamber, said fluid comprising a mixture of a dialkyl monoaryl phosphate ester as hereinbefore described and a dialkyl ester of an aliphatic dicarboxylic acid as hereinbefore described. In such a hydraulic apparatus wherein a movable member is actuated by the above described functional fluid, performance characteristics are obtainable which are superior to those heretofore obtainable.

Because of the excellent flammability characteristics of the functional fluids of this invention, their exceptionally low pour points, and high inherent lubricity, the functional fluids of this invention may be utilized in those hydraulic systems wherein power must be transmitted and the frictional parts of the system lubricated by the hydraulic fluid utilized. Thus, the novel functional fluids of this invention find exceptional utility in the transmission of power in a hydraulic system having a. pump therein supplying the power for the system. In such a system, the parts which are so lubricated include the frictional surfaces of the source of power, namely the pump, valves, operating pistons and cylinders, fluid motors, and in some cases, for machine tools, the ways, tables and slides. The hydraulic system may be of either the constant-volume or the variable-volume type of system.

The pumps may be of various types, including the piston-type pump, more particularly the variable-stroke piston pump, the variable-discharge or variable displacement piston pump, radial-piston pump, axial-piston pump, in which a pivoted cylinder block is adjusted at various angles with the piston assembly, for example, the Vickers Axial-Piston Pump, or in which the mechanism which drives the pistons is set at an angle adjustable with the cylinder block; gear-type pump, which may be spur, helical or herringbone gears, variations of internal gears, or a screw pump; or vane pumps. The valves may be stop valves, reversing valves, pilot valves, throttling valves, sequence valves or relief valves. Fluid motors are usually constantor variable-discharge piston pumps caused to rotate by the pressure of the hydraulic fluid of the system with the power supplied by the pump power source. Such a hydraulic motor may be used in connection with a variable-discharge pump to form a variablespeed transmission.

What is claimed is:

1. A functional fluid comprising essentially a mixture of 25 to parts by weight of dialkyl monoaryl phosphate ester having the formula wherein R1 and R2 each represents an alkyl radical containing from 1 to 18 carbon atoms, and R3 represents an aryl radical, and 10 to 75 parts by weight of dialkyl ester ofian aliphatic dicarboxylic acid having the formula R-1OOC(CH2)nCOOR5 wherein R1 and R2 each represents an alkyl radical containing from 4 to 14 carbon atoms, and R3 represents a phenyl radical, and 10 to 50 parts by weight of dialkyl ester of an aliphatic dicarboxylic acid having the formula wherein R4 and R5 each represents an alkyl radical containing from 4 to carbon atoms, and n is an integer from 2 to 8 inclusive.

3. A functional fluid comprising essentially a mixture of 50 to 90 parts by weight of octyl butyl phenyl phosphate and 10 to 50 parts by weight of dialkyl ester of an aliphatic dicarboxylic acid having the formula wherein R4 and R each represents an alkyl radical contaming from 4 to 10 carbon atoms, and n is an integer from 2 to 8 inclusive.

4. A functional fluid comprising essentially a mixture of to parts by weight of 2-ethylhexyl n-butyl phenyl phosphate and 10 to 50 parts by weight of di-isoamyl adipate.

5. A functional fluid comprising essentially a mixture of 50 to 90 parts by weight of n-octyl n-butyl phenyl phosphate and 10 to 50 parts by weight of di(2-ethylbutyl) adipate.

6. A functional fluid comprising essentially a mixture of 50 to 90 parts by weight of 2-ethylhcxyl sec-butyl cresyl phosphate and 10 to 50 parts by weight of diamyl adipate.

7. A functional fluid comprising essentially a mixture of 50 to 90 parts by Weight of Z-ethylhexyi capryl phenyl phosphate and 10 to 50 parts by Weight of di(6-mcthylheptyl) adipate.

8. A functional fluid comprising essentially a mixture of 50 to 90 parts by weight of Z-ethylhexyl n-butyl phenyl phosphate and 10 to 50 parts by weight of di(2-ethylhexyl) sebacate.

References Cited in the file of this patent UNITED STATES PATENTS 2,342,414 Magill Feb. 22, 1944 2,481,372 Von Fuchs et al. Sept. 6, 1949 2,512,582 Plueddeman June 20, 1950 2,542,785 Walker Feb. 20, 1951 'FoRErGN PATENTS 457,548 Great Britain Aug. 24, 1935 524,937 Great Britain Aug. 19, 1940 

1. A FUNCTIONAL FLUID COMPRISING ESSENTIALLY A MIXTURE OF 25 TO 90 PARTS BY WEIGHT OF DIALKYL MONOARYL PHOSPHATE ESTER HAVING THE FORMULA 